I have been playing Sims2 for a while now and I've only had a sim abducted once or twice, naturally. So it's pretty rare. If you want an alien baby then all you have to do is follow these steps...
1. Copy this exactly: BoolProp Testingcheatsenabled true
2. Go into Sims 2 and open up the cheat box (ctrl+shift+c)
3. Paste (ctrl+v) the BoolProp yadayada thing in to the cheat box. Make sure not to do a space or anything before it.
4. I suggest doing this at night (you can do it at day but it makes it weird). Select a male adult sim (the one you want to have a baby) then shift+click the telescope. Two options should come up. Click the one that has 'get abducted' in it.
5. Then make the man look through the telescope. If you've done everything right he should get abducted and then come back pregnant.
Oh and by the way when you do the BoolProp Testingcheatsenabled true cheat if you shift-click on the mailbox or a person loads of options come up. You can also shift-click on most things and an option will come up 'force error' this will delete the object. But you can do different things with different objects. If you click on the T.V., stereo or computor you can break them, you can restock the fridge, if you click on the bath, a sink, toilet or counter you can set the state of their cleanliness. And I'm sure there's a few other things. Have fun!
If you want an easy 1,000 Simolens, open up the cheat window (Shift + Ctrl + C) and type in kaching.
If you want an easy 50,000 Simolens, open up the cheat window (Shift + Ctrl + C) and type in motherlode.